1. Field of the Invention
The present invention relates in general to solenoid drivers and in particular to a short circuit proof driver and alarm circuit for a solenoid in a glassware forming machine.
2. Description of the Prior Art
The individual section glassware forming machine is well known and includes a plurality of sections, each having means for forming glassware articles in a timed predetermined sequence of steps. Typically, the sections are fed from a single source of molten glass. The source forms gobs of molten glass which are distributed to the individual sections. The sections are operated in synchronism at a relative phase difference such that one section is receiving a gob while another section is delivering a finished glassware article to a conveyor and one or more other sections are performing various ones of the intermediate forming steps.
Typically, an electronic control means is utilized to synchronize the operation of the individual sections. The forming means in each individual section are operated by pneumatic motors or actuators. The electronic control means generates control signals through an interface circuit to actuate solenoid-controlled valve blocks which operate the forming means. Such a control system is disclosed in U.S. Pat. No. 4,152,134.
Solenoid driver circuits which have been utilized in prior art glassware forming machines have been subject to destruction caused by short circuits in the controlled solenoid. Such short circuits occur frequently in older machinery, resulting in excessively high current being drawn through the solenoid driver circuit. Also, a short circuit can occur in a cable connecting the solenoid driver to the controlled solenoid in the valve block, resulting from normal fatigue or accidental injury to the cable. Such an occurrence could activate a solenoid unintentionally, causing mechanical motion in the glassware forming machine and the possibility of injury to an operator working on the machine.